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    slub: consider pfmemalloc_match() in get_partial_node() · 8ba00bb6
    Joonsoo Kim 提交于
    get_partial() is currently not checking pfmemalloc_match() meaning that
    it is possible for pfmemalloc pages to leak to non-pfmemalloc users.
    This is a problem in the following situation.  Assume that there is a
    request from normal allocation and there are no objects in the per-cpu
    cache and no node-partial slab.
    
    In this case, slab_alloc enters the slow path and new_slab_objects() is
    called which may return a PFMEMALLOC page.  As the current user is not
    allowed to access PFMEMALLOC page, deactivate_slab() is called
    ([5091b74a: mm: slub: optimise the SLUB fast path to avoid pfmemalloc
    checks]) and returns an object from PFMEMALLOC page.
    
    Next time, when we get another request from normal allocation,
    slab_alloc() enters the slow-path and calls new_slab_objects().  In
    new_slab_objects(), we call get_partial() and get a partial slab which
    was just deactivated but is a pfmemalloc page.  We extract one object
    from it and re-deactivate.
    
      "deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly.
    
    As a result, access to PFMEMALLOC page is not properly restricted and it
    can cause a performance degradation due to frequent deactivation.
    deactivation frequently.
    
    This patch changes get_partial_node() to take pfmemalloc_match() into
    account and prevents the "deactivate -> re-get in get_partial()
    scenario.  Instead, new_slab() is called.
    Signed-off-by: NJoonsoo Kim <js1304@gmail.com>
    Acked-by: NDavid Rientjes <rientjes@google.com>
    Signed-off-by: NMel Gorman <mgorman@suse.de>
    Cc: David Miller <davem@davemloft.net>
    Cc: Chuck Lever <chuck.lever@oracle.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    8ba00bb6
slub.c 129.8 KB